The present invention relates to a method of reducing phosphorus pollution from agricultural runoff. The present invention also relates to a method of immobilizing bio-available phosphorus in organic waste products using high phosphorus affinity material capable of forming insoluble metal-phosphorus complexes. In addition, the present application relates to a method of making fertilizer comprising a designated amount of phosphorus
Although the evidence is circumstantial and inconclusive at this point, it has been suggested that nutrients lost from farm lands through runoff and leaching may be partially responsible for the outbreaks of Pfiesteria-like organisms in various rivers along the Atlantic coast. Nutrients enter water from many sources. Sewage sludge, septic tank effluent, organic manufacturing waste, and animal manure contain high concentrations of nitrogen and phosphorus.
Farmers commonly obtain nutrients for their crops from inorganic commercial fertilizers and from organic sources such as animal manure and biosolids from wastewater treatment plants. Generally, inorganic nitrogen and phosphorus compounds are water soluble and readily available to plants. In contrast, most organic nutrient sources contain both inorganic forms of nutrients and forms that must first be mineralized or decomposed to become available to plants. The movement of nitrogen and phosphorus through soil are different. If nitrogen is converted to the highly water soluble nitrate-nitrogen form, and is not used during plant growth, it can move through the soil-water system and be vulnerable to leaching into the groundwater. In the same way, soils amended with large quantities of organic or inorganic phosphorus may generate significant amounts of soluble phosphorus that can be readily transported by surface and subsurface runoff and groundwater leachate.
When organic sources of nutrients are used, the ratios of nitrogen and phosphorus do not usually correlate with the crop's actual nutrient needs. The phosphorus to nitrogen ratio required by plants (1:6) is usually much smaller than the ratio found in manure (1:1-1:2). Hence, nitrogen-based application of manure to agricultural fields results in the application of phosphorus in excess of plant nutrient requirements.
In animal waste, phosphorus occurs in both dissolved (soluble) and particulate forms. Phosphorus losses from agricultural systems, other than by crop removal, generally occur through the following pathways associated with surface water runoff: a) particulate losses either as phosphorus absorbed into soil particles or organic materials, and/or b) soluble inorganic and organic phosphorus compounds.
Various methods have been suggested to reduce soil erosion, which also reduces particulate phosphorus in runoff. These are, among others: no-till farming, contour/strip cropping, grass waterways, buffered streams, and related structural controls. While efforts to reduce sediment in agricultural runoff often reduce particulate phosphorus, they do not reduce losses of dissolved phosphorus, thus increasing the percentage of total phosphorus in runoff that is immediately available for biological uptake. Consequently, recent efforts on improving water quality of surface waters has focused on reducing soluble, bioavailable dissolved phosphorus.
With commercial fertilizers, it is possible to tailor the ratios of nitrogen and phosphorus to meet the crop's nutrient needs. In the past, organic nutrient sources were typically applied to the soil to meet the crop nitrogen requirements, without regard for the phosphorus content in the soil. Nitrogen-based plans have made use of animal wastes, been cost effective, and reduced nitrogen application to land. However, this has resulted in overapplication of phosphorus. These applications frequently occur on soils with that already have high phosphorus content caused by repeated, long-term applications of organic fertilizers. This overapplication increases the potential for phosphorus to move from farmland to nearby water.
One method to reduce soluble phosphorus in runoff and leachate is to base application rates of organic fertilizer sources on the recommended crop phosphorus requirements. Phosphorus-based nutrient management plans can be applied to fields with a very high potential for phosphorus loss to surface water. However, using P-based application of organic fertilizers results in underapplication of nitrogen. In such a situation, additional nitrogen from other sources—most likely commercial nitrogen fertilizers—must be added to supplement the fertilizer. Thus, there is a necessity to develop a system that allows for the optimum use of organic sources of nutrients while maintaining environmental integrity.
In Maryland, soil test phosphorus values will be the critical factor in determining whether animal manure can be applied according to crop nitrogen requirements. For soils that test in the “excessive phosphorus” range, nutrient managers are required to perform a Phosphorus Site Index (PSI) assessment (The Maryland Phosphorus Site Index: A Technical User's Guide (Version I). August 1999. Agricultural Nutrient Management Program and MD Cooperative Extension. Univ. of MD, College Park, Md., which is incorporated herein by reference in its entirety). The PSI takes into consideration factors such as soil test phosphorus, soil type, fertilizer source and phosphorus availability, slope, buffer strips, runoff potential and cropping methods to derive a final rating based on the potential for phosphorus loss to surface waters. The final rating is based on 5 categories (high risk to low risk) on which phosphorus application guidelines are based. A low risk rating will allow for the continued application of manure based on nitrogen requirements, while a medium to high risk rating indicates that phosphorus applications will either be limited to annual crop requirements or eliminated completely.
While phosphorus based application rates of organic fertilizers would be environmentally sound and should begin to limit both phosphorus and nitrogen enrichment of the associated water bodies, this type of planning would have a very serious and potentially expensive impact on farms that generate or use animal manure. Adopting phosphorus-based nutrient management plans would increase operation and crop production costs. Major changes to current farming practices would involve importing of fertilizer nitrogen and exporting of manure. These types of activities can have a significant negative impact on the profitability of any farming system.
Among the significant contributors to the fertilizer industry are the poultry growers. In the poultry industry, approximately 625 million birds (three billion pounds of meat) are raised each year on the Delmarva Peninsula Assuming these flocks are fed according to the National Research Council recommendations, 53 million pounds of manure nitrogen and 22 million pounds of manure phosphorus are excreted per year. Poultry farming therefore represent one of the significant sources of nutrients that have a potential impact on water resources.
Many of the lower Eastern Shore counties in Maryland have inadequate cropland available for efficient utilization of manure phosphorus, therefore, alternative disposal options have been suggested. Transporting nutrients to areas of the state or region where soils do not contain excessive concentrations of phosphorus and where phosphorus inputs are necessary for optimum crop production is one solution. However, distribution is not so much limited by lack of available technology but rather by the economics of transporting manure long distances.
Burning manure is another disposal option. In the early 1980's, Delmarva Power burned broiler litter in their Indian River Generation Facility at Millsboro, Del. However, litter supply still remains a problem. The BTU value of broiler litter is about 6,800 BTU's per pound at 30 percent moisture in a large fluid bed burner. The ash content for broiler litter is approximately 11.3 percent. This shows a large volume and weight reduction. Burning raw litter in small on-farm furnaces has presented some problems such as slag formation because of incomplete combustion, odors, particulate, and loading difficulties.
Regardless of any other measures either to reduce the phosphorus content of manure or to find alternative uses for manure, these actions will have no effect on soils that already have high phosphorus levels and are at risk for phosphorus losses to the surrounding environment through surface water. However, remediation of high-phosphorus soils has never been implemented on a large scale. Hence, no standard practice exists.
Methods of removing excess phosphorus from the soil include using crops, and tillage methods. Since plants take up phosphorus, growing crops without adding phosphorus to the soil provides an income source (crops) and leaves the soil undisturbed. However, this process will require the application of nitrogen, which is an expense to the farmer, as well as having a pollution potential of its own.
A novel variation of mining phosphorus through crop removal, called phytoremediation, is being explored for removing inorganic contaminants from soil. Phytoremediation, or “Green Remediation” uses unusual plants that have developed the ability to concentrate high levels of elements, usually heavy metals, in plant tissue. The primary limitation of phosphorus phytomining is no one has identified reliable phosphorus hyperaccumulators.
Tillage, an immobilization technique, would place the phosphorus-rich surface soil well below the surface and out of reach of surface runoff water, hence effectively stopping surface transport of phosphorus. The phosphorus would be below the surface but still within the root zone, enabling it to be taken up by plants over time. One major concern is that the soil that would be brought to the surface must be equally good for crop production, or else, it would create a permanent liability for the farmer. Furthermore, the subsurface soils that are brought to the surface must also be low in phosphorus or tillage will have no impact. The ramification of this is that extensive soil testing of the deeper soil would be necessary prior to performing tillage, and it would not be suitable on some farms.
Thus, there exists a need in the agriculture field for a more effective and cost-efficient method for immobilizing phosphorus without harming the environment.
Turning to an unrelated field, in the metal refining or manufacturing industry, byproducts are considered environmental hazards. In the titanium dioxide pigment manufacturing process, for example, there can be mentioned two refining or manufacturing methods—sulfuric acid and chlorine. Both of these known industrial methods, however, involve environmental pollution, although the chlorine method pollutes somewhat less.
The sulfate method is a relatively low-technology, batch manufacture process, and is described in U.S. Pat. No. 4,186,088, which is incorporated herein by reference in its entirety. The sulfuric acid method is advantageous for refining titanium because the starting titanium-containing material is not particularly limited, and an ore having a titanium oxide content of 50 to 60% by weight, for instance, ilmenite, can be used as the starting material. But large quantities of wastes are formed. More specifically, it is said that 3 to 4 tons of iron oxide hydrate and about 8 tons of dilute sulfuric acid are formed for 1 ton of titanium oxide produced. Environmental concerns prohibit discarding these wastes formed in such large quantities into rivers or seas. Further, if these wastes are treated again in a particular treatment plant to recover valuable resources, the manufacturing cost is inevitably increased. It is said that the manufacturing cost is increased by about 15% by this treatment of the wastes.
The chlorine method, on the other hand, is a relatively high technology, continuous process. If the chlorine method is adopted for the production of titanium oxide, the problem of wastes is not so acute. The raw material used in the method is typically a rutile ore having a titanium oxide content of at least 90% by weight. A high purity rutile ore such as mentioned above is reacted with chlorine gas to form titanium tetrachloride, which is reacted with oxygen to form titanium oxide and chlorine. The byproducts of these industrial metal-refining processes are typically rich in iron.
The metals refined by the above processes are filtered, washed, and dried. The dried pigments are treated with organic solvents, ground, and packed or slurried with appropriate dispersants.
The chlorine and sulfuric acid processes for making metal oxides, such as TiO2, are described in Braun et al., “TiO2 pigment technology: a review,” Progress in Organic Coatings, 20, 105-138 (1992), and Braun, “Titanium Dioxide—A Review,” Journal of Coatings Technology, Vol. 69, No. 868, 59-72, (1997), which are incorporated herein by reference in their entirety.
The discharges of the metal refining process, such as in the titanium dioxide pigment manufacturing process discussed above, which include iron compounds, dilute acids and miscellaneous inorganic contaminants of the ore, have become international environmental issues. The cost of waste disposal has been responsible for large increases in the manufacturing costs of the pigments made from titanium dioxide. Currently, these byproducts are disposed of in landfills. This is not a satisfactory solution to the waste disposal problem because landfilling the byproduct does not benefit the environment and is costly to the manufacturing companies.
Offiah, O. and D. S. Fanning. 1994. Liming value determination of a calcareous, gypsiferous waste for acid sulfate soil. J. Environ. Qual. 23:331-337 discloses adding lime to calcareous and gypsiferous soil to raise the pH of the soil. However, the reference does not disclose removing phosphorus from the soil using the calcium and iron containing mixture such as an industrial byproduct of a metal refining or manufacturing process of the invention.
Hughes, K. J. and L. R. Cooperband. 1998. SWAN-gypsum as a potential soil amendment for reducing phosphorus in a constructed wetland receiving milking parlor effluent. 1998 Annual meeting abstracts. ASA, CSSA and SSSA. Baltimore, Md. October 18-22, is directed to mixing SWAN-gypsum with a constructed wetland soil. However, the reference does not disclose using the inventive composition as a direct additive to agricultural soil, animal waste, or liquid waste to remove phosphorus.
Hsu, P. H. 1976. Comparison of iron (III) and aluminum in precipitation of phosphate from solutions. Water Research. 10:903-907, reported that the optimum phosphorus removal by Fe occurred in the pH range of (4.1-7.1), while optimum phosphorus removal by Al occurred in the pH range of (5.5-8.0). However, the reference does not disclose using the inventive composition for treating agricultural soil, animal waste, or liquid waste to remove phosphorus.
Cooke, G. D. et al. 1986. Lake and reservoir restoration. Ann Arbor Science Book, Boston, Mass. also demonstrated phosphorus removal by sorption on aluminum hydroxide surfaces in a pH range of 6 to 8. Even in solutions with low concentration of Ca2+, phosphorus removal can occur via adsorption onto calcite surfaces. However, the reference does not disclose using the inventive composition for treating agricultural soil, animal waste, or liquid waste to remove phosphorus.
Moore, Jr., P. A., and D. M. Miller. 1994. Decreasing phosphorus solubility in poultry litter with aluminum, calcium and iron amendments. J. Environ. Qual. 23: 325-330 is directed to methods for reducing soluble phosphorus in poultry litter with aluminum, calcium and iron amendments. However, the reference does not disclose using the inventive composition for treating agricultural soil, animal waste, or liquid waste to remove phosphorus.
EP 0 650 515 B1 discloses producing a binding agent made of gypsum, titanium hydroxide and iron hydroxide compounds that are used for stabilizing and strengthening soil or clay so that buildings can be constructed on the modified soil. The reference is unconcerned with phosphorus removal.
Barksdale, Titanium, Its Occurrence, Chemistry, and Technology, second edition, The Ronald Press Co., NY (1966), describes the chemistry of titanium as well as the sources of titanium and its extraction and manufacture. This reference is incorporated herein by reference in its entirety.
Fitch et al. (U.S. Pat. No. 4,186,088) is directed to a process of neutralizing the waste stream from a sulfuric acid-based extraction procedure from titanium containing ores. A byproduct of the secondary neutralization operation, in particular, has neutral pH and has low concentrations of metals, excluding iron which is present at levels in excess of 10%. The patent does not discuss removing phosphorus from animal waste using the byproducts that are described. U.S. Pat. No. 4,186,088 is incorporated herein by reference in its entirety for its description of the process of neutralizing the waste stream obtained through the titanium extraction process, thereby obtaining the byproduct Secondary Waste Acid Neutralization, or SWAN, gypsum.
Thus, there remains a need in the farming, animal growing and nutrient management industries for a method of removing or immobilizing bio-available phosphorus from animal waste such as poultry litter so that such animal waste can continue to be applied to the field and used as primary nitrogen source for crops, while minimizing loss of phosphorus to surface water. There is also a need in the metal oxide manufacturing industry, such as titanium dioxide, for an environmentally safe and cost-effective method of disposing of industrial byproducts.